The invention relates to a vapor lead-through system for a rotary evaporator and to a rotary evaporator.
Such vapor lead-through systems are already known, in which a vapor lead-through system connected to the evaporator flask is surrounded and driven by a drive part. The vapor lead-through system is led via a seal into or onto a static cooler. With this arrangement, the seals on account of the rotation are mechanically loaded and must be regularly replaced in order to guarantee the functioning and operational safety.
EP 504 099 shows an at least two-part vapor lead-through tube with which the end-faces of the static part as well as the rotatable part in contact with the drive part are formed as sealing surfaces, wherein materials which are as low-wear and as resistant as possible such as plastic materials are combined with ceramic or glass materials.
A disadvantage of the known vapor lead-through systems lies in the fact that the rotatable vapor lead-through tube is in direct contact with the drive part. The movement of the drive part which is in no way exactly concentric, leads to eccentric forces which act directly on the vapor lead-through tube. As a result, mechanical loading of the seals occurs.
DE 15 19 744 shows a vapor lead-through tube connected to the drive part, with a seal which is rigidly held by the radial extension of a flange but is held in a radially compensating manner between the sealing surfaces of the cooler and drive part. The radial sliding movement arising by way of this leads to a corresponding mechanical loading.
It is the object of the invention to avoid the disadvantages of the prior art, in particular thus to provide a vapor-lead-through system and a rotary evaporator with which eccentric forces on the seals are minimized and the wear resistance is increased.
According to the invention this object is achieved with a vapor lead-through system and with a rotary evaporator as described below.
By subdividing the vapor lead-through into a connection piece which is drivable with the drive part and connected or connectable to the evaporator vessel, and into a vapor lead-through tube rotatably mounted in a seal stationary with respect to a cooler, forces arising from the drive part act mainly upon the connection piece and where appropriate only on the evaporator-side end of the vapor lead-through tube. The transmission of eccentric forces from the connection piece in connection with the drive part onto the seal stationary with respect to the cooler is minimized in that the vapor lead-through tube is connected to the connection piece in a manner such that its axis is movable with respect to the axis of the connection piece. The vapor lead-through tube with respect to the stationary seal is, to a certain extent, decoupled from the drive piece.
It is particularly advantageous when the stationary seal bears sealingly on the outer wall of the vapor lead-through tube and has been manufactured in such a way and from such material that even under a heat and chemical effect it does not change in shape or pretension. This modified material, for example PTFE, also permits the stationary seal, during operation, to bear optimally at all times on the vapor lead-through tube. The independence of the vapor lead-through tube on the evaporator-side end, of an eccentric movement of the drive part, permits the application of such materials in the stationary seal since these also with eccentric movement of the drive part are only minimally mechanically loaded.
A stationary seal of an inert, friction-modified plastic, in particular PTFE, is particularly suitable for this. By way of the restoring properties of this PTFE reversible deformability is ensured. Furthermore PTFE is chemically resistant with regard to solvent-containing vapors and is friction-modifiable, by which means the mechanical loading by way of friction may be minimized.
Of course also other materials with suitable properties are conceivable.
It is particularly advantageous when the seal is held in a base body of an inert plastic, in particular PTFE.
A mounting of the stationary seal in a base body of an inert plastic has several advantages. The base body may likewise assume sealing functions. In particular the cooler-side end-face of the base body may be arranged such that it bears sealingly on a cooler-side connection piece.
A base body of an inert plastic, in particular PTFE, is particularly suitable, since various regions of the base body may be directly exposed to the solvent-containing vapors.
According to a preferred embodiment of the invention one design of the stationary seal as an annular body with a deformable lip is particularly favorable. Thereby the deformable lip assumes the sealing function and the annular body acts in a stabilizing manner.
Additional stability of the stationary seal is achieved by providing a first ring, in particular a steel ring, on the outer periphery of the base body and/or a second ring, in particular a steel ring, in the seal. Materials other than steel, which sufficiently stabilize the seal, might also be used.
The vapor lead-through tube may on the evaporator-side end be mounted in a seal whereby the outer wall of the vapor lead-through tube sealingly bears on the inner side of the seal.
Particularly suitable is an evaporator-side seal which in cross section is formed V-shaped. The inner and outer limbs of such a seal may be formed as sealing surfaces.
It is particularly advantageous when the evaporator-side seal on its outer side comprises a spherical surface and the connection piece comprises a taper-ground joint, wherein the spherical surface of the seal while forming a ball joint lies sealingly in the taper-ground joint of the connection piece. The ball joint permits in a particularly simple manner a movability of the evaporator-side seal to the connection piece and thus a compensation of an eccentric movement of the connection piece at the evaporator-side end of the vapor lead-through tube. Eccentric forces which occur at the connection piece being in connection with the drive part are thus particularly effectively compensated. Conceivable is also a kinematic reversal so that the vapor lead-through tube via a taper-ground joint bears on the outer side of the evaporator-side seal and the connection piece comprises a conical surface which is in contact with the inner side of the seal.
The evaporator-side seal preferably consists of an inert plastic, in particular PTFE, since this material has the required thermal resistance and solvent resistance. Conceivable however are also all other materials which have the mentioned properties.
An O-ring within the evaporator-side seal may be advantageous for the stability of the sealing arrangement. Particularly suitable is a rubber ring since it has the necessary elasticity in order to dampen radial forces in the ball joint.
By providing a stop in the axial direction on the evaporator-side end of the vapor lead-through tube, axial displacement of the vapor lead-through tube, in particular with a manipulation on the apparatus, may be avoided. The stop may be particularly simply realized when the vapor lead-through tube comprises a flange which is latchable on a retaining element on the drive part, e.g. in a groove with an O-ring. Other forms of the stop are possible.